The same thing happened to me when I first got my Buick, back in 2000. In my case, the Powermaster was failing (and I knew ZERO about it) and had leaked brake fluid down the frame rail, and I must have driven over it, because the car fishtailed like I had never experienced before, and next thing I knew I was up against the curb with a broken axle.
I did what Nick said: replaced axles (Moser stock replacements), bearings, and seals, and the pass backing plate, and 15 years & 30k miles later, no issues to report. I also got to replace the Powermaster - that almost made me sell the car.
I learned tons of stuff about the car that month. Good luck with your repair.